Develop transgenic animal models that are informative for understanding chronic inflammation in humans. Macrophages play a key role in the pathogenesis of multiple chronic inflammatory diseases. Studies using knockout mice have allowed investigators to examine the important role of macrophage-specific genes. However, these studies are limited to genes expressed in multiple tissues, as macrophage-specific knockout mice are not available. Since the loss of a gene may prevent the differentiation or migration of the monocyte prior to its actual arrival at the site of injury, the generation of an inducible, macrophage-specific knockout is preferable to study chronic inflammatory diseases. Our laboratory has developed a new transgenic mouse model targeting Cre recombinase expression in tissue macrophage, using the scavenger receptor A promoter (SRA-Cre). After its induction with tamoxifen, Cre will cleave any "floxed" gene in macrophages. Our model will also allow to knockout genes at any stage of the disease. The main goal of our proposal is to characterize this new conditional mouse model, using three aims. In the first aim, SRA-Cre mice will be crossed into a reporter line, and specificity and inducibility of Cre expression will be assessed in three models of lung injury (cigarette smoke exposure, asthma, and acute lung injury). In the second aim, SRA-Cre mice will be crossed into the apolipoprotein-E (Apoe) knockout background. Atherosclerotic plaques will be analyzed for expression of Cre in lesion macrophages and foam cells. This macrophage-specific Cre- expressing Apoe knockout model will be made available to laboratories studying the function of macrophages in atherosclerosis. In a third aim, we will generate of a conditional, macrophage- specific Tissue Inhibitor of Metalloproteinase-3 (Timp-3) knockout model. TIMP-3 is expressed in macrophage and plays an important role in inflammatory diseases. However, global Timp-3 knockout mice exhibited developmental abnormalities in the lung and the heart. We have generated a floxed Timp-3 model, which will be crossed into the SRA-Cre background. Utilizing this model, we will determine how the absence of TIMP-3 in macrophages affects lung injury due to cigarette smoke. Our new conditional, macrophage-specific targeting model will be a highly valuable tool, allowing researchers to precisely assess the roles and functions of genes expressed by macrophages during chronic inflammatory diseases. PUBLIC HEALTH RELEVANCE: Macrophages play a key role in the pathogenesis of multiple chronic inflammatory diseases. In this proposal, we will characterize a newly developed conditional, macrophage-specific mouse model, where Cre recombinase is regulated by the scavenger receptor A promoter. Our model will allow to knockout genes of interest only in macrophages and at any stage of the disease. The major goal of our proposal is to generate a mouse model that will allow researchers to specifically and conditionally knockout genes of interest in macrophages during chronic inflammatory diseases. This model will be a highly valuable model, allowing researchers to precisely assess the roles and functions of genes expressed by macrophages during chronic inflammatory diseases. In addition, we propose to cross this model into the atherosclerosis-prone Apoe knockout model, to allow examination of macrophage genes in this important vascular disease. We will also examine the consequences of the absence of macrophage tissue inhibitor of metalloproteinases-3 in lung injury.